1. Technical Field
The present invention relates generally to metal gaskets. The invention relates more particularly to metal gaskets having a rigid seal. Most particularly, the invention relates to a metal gasket having a rigid seal that varies in thickness and width along its length.
2. Related Art
In sealing applications associated with extreme pressure and/or temperature environments, such as various sealing applications in internal combustion engines (i.e., head gaskets, exhaust manifold gaskets, turbocharger gaskets, etc.), multilayer metal gaskets with elastically deformable embossments have been utilized to provide the required fluid seals. Three common issues exist with multilayer metal gaskets, such as multilayer steel cylinder head gaskets, the fatigue resistance of the gaskets, load relaxation and joint distortion associated with the use of the gaskets. Multilayer metal gaskets are made from thin sheets of metal, such as steel. In many applications, such as cylinder head gasket applications, these multilayer metal gaskets are subjected to temperature and pressure extremes associated with the operation of the internal combustion engine and the environmental conditions under which it is utilized. Thus, as the engine is operated, the internal combustion processes subject the cylinder head gasket to repeated pressure-induced cyclic motion and stresses and extreme temperatures. Over the operating life of an engine, this cyclical motion and stresses at the extreme operating temperatures can cause fatigue within the metal gasket, particularly fatigue in the region of the embossments which are used to provide the sealing surfaces of the gasket. While a cylinder head gasket is used as an example, other applications of multilayer metal gaskets are also subject to cyclic pressures and temperatures associated with their operating environment, and are thus also subject to the fatigue processes described above.
In the case of multilayer metal gaskets used in cylinder head gasket applications, this motion, and associated load change, within the cylinder head gasket is known to play a significant role in cylinder bore distortion because the cylinder head gasket is the interface between the cylinder bore located within the engine block and the cylinder head. In operation, the cyclic motion described above also results in distortion of the cylinder bore in the region of the gasket. Cylinder bore distortion can cause high rates of wear on the piston rings or combustion gas blow-by within the head gasket.
One of the primary factors effecting fatigue is the fact that an embossment must be added to the cylinder head gasket to redistribute the available bolt load to produce a uniform sealing force along the length of the sealing feature of the cylinder head gasket. This embossment reduces the stiffness of the joint and exacerbates joint motion. As the gasket is subjected to cyclic temperatures and pressures, this can result in a tendency for fatigue failures at locations within the gasket where the magnitudes of the motions are highest. Further, the sealing forces associated with such gaskets are known to change as a function of time related to the cyclic motion and associated creep-induced stress relaxation processes.
One example of a multilayer metal gasket that is designed to address the issues described above is described in US 2003/0080514 A1 which is directed to combustion stopper seal having a variable thickness and width flange directly adjacent to the combustion cylinder opening and a method of making the stopper seal. The stopper seal is associated with a stopper layer of a multilayer metal gasket. The stopper seal is adapted to make the sealing pressure within the functional or sealing layers which contain the sealing embossments more uniform. However, the elastic nature of the embossments still permits undesirable motion within a seal joint which utilizes such a stopper layer, and also incorporates the associated inherent complexity of a multilayer metal gasket design.
Given the limitations associated with multilayer metal gaskets, it is desirable to develop new metal gasket designs and seal joint configurations which greatly reduce or eliminate cyclic motion within the seal joints due to the inherent characteristics of the gasket. It is also desirable to reduce the complexity of metal gaskets as compared to existing multilayer metal gasket configurations, by reducing the number of layers and associated elements. Further, it is also desirable to make the sealing force along the seals more uniform by controlling the sealing force along the length of the sealing surface of the gasket. Still further, it is desirable to develop gasket and seal configurations which have improved resistance to fatigue and relaxation of the sealing force as the seal joint is subjected to use and the application cyclic forces to the joint.